1. TW2 has been in development for a long time, it is not built on DX11 at its core. It still has win XP support. Consoles support DX9 level effects, they just can't have as high res textures and so on.

2. It is not an FPS, meaning they need to use resources for a lot of other things than just graphics. If they focused only on graphics the game would probably suck.

3. Most people ( because of the interface for one thing ) thinks it is prepared for a console release.

4. They can't make system specific optimizations which you can for console games, making the difference much less than it could be.